Carbon dioxide (CO2) is a major greenhouse gas with significant contribution to global warming (Halmann and Stenberg 1999). Removal of CO2 from different gas streams is becoming increasingly important for various applications like treatment of flue gas, natural gas, biogas, and hydrogen purification as well as closed-circuit breathing systems (CCBS) for use in confined spaces such as manned space shuttles (Satyapal et al. 2001), and in emergency situations. The recovered CO2, with different degrees of purity, also has numerous applications in the chemical industry.
Separation, capture and storage of carbon dioxide (CO2) have received significant attention in recent years. Liquid phase absorption in amine solutions has been widely used to treat gases with medium to high CO2 concentration, but due to the high regeneration cost of the absorbent and corrosion problems (Veawab et al. 1999), it is highly desirable to develop less energy intensive technologies like adsorption (Ruthven 1994) and membrane separation (Hong et al. 2008).
Many of CO2 adsorbents have been developed in recent years including metal oxides (Wang et al. 2008), zeolites (Goj et al. 2002; Cavenati et al. 2006; Akten et al. 2003; Belmabkhout et al. 2007), carbon (Himeno et al. 2005), metal-organic frameworks (MOFs) (Millward and Yaghi 2005; Bourrelly et al. 2005; Yang et al. 2008; Yang and Zhong 2006; Li and Yang 2007), organo-silicas and surface-modified silicas (Harlick and Sayari 2007; Comoti et al. 2007) as well as membrane technology (Sridhar et al. 2007; Hong et al. 2008).
Ideally, an adsorption medium for CO2 removal at ambient temperature should combine (i) high CO2 uptake, (ii) complete regeneration under mild condition, (iii) high thermal stability, and (iv) favourable adsorption-desorption kinetics.
The discovery of periodic mesoporous materials like MCM-41 silica has resulted in extensive research activity on their synthesis and applications, particularly for separation and catalysis (Sayari 1996; Sayari and Jaroniec 2008). It is intriguing that despite the significant growth in the area of periodic mesoporous materials (for a review see Sayari (2003) and references therein), there are only few studies devoted to CO2 adsorption on materials like MCM-41 silica (Branton et al. 1995; Morishige et al. 1997; Morishige and Nakamura 2004; Sonwane et al. 1998). The early studies by Morishige et al. (1997, 2004) and Sonwane et al. (1998) focused on high pressure CO2 adsorption at temperature below 273 K for the purpose of structural characterization. He and Seaton (2006) studied low pressure adsorption of pure CO2 and CO2—CH4 mixture for the characterization of MCM-41 surface heterogeneity. Although, the use of organically-modified silica materials for CO2 removal was extensively studied using different mesoporous silica supports such as MCM-41, SBA-15, MCM-48 and pore-expanded MCM-41 (for a review see Harlick and Sayari (2007) and reference therein); adsorption of CO2 was investigated in a limited range of CO2 concentration, temperature and pressure. The patent application WO 2008/081102 (Pirngruber et al. 2008) discloses the use of metal-organic frameworks (MOFs) having a pore diameter in the range of 0.5-5 nm and surface area the range of 2000-4000 m2/g, for hydrogen purification and carbon dioxide recovery at pressure higher than 4 bar.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.